Support Python 3.10

[tari]

nosetests is no longer supported upstream and broken on Python 3.10, so this requires migrating to something else, where I've chosen pytest to run doctests and manually using coverage otherwise. One ABC used from collections moved to collections.abc in Python 3.2, which can safely be updated.

[codecov[bot]]

Codecov Report

Merging #189 (2524668) into master (0578729) will decrease coverage by 0.47%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #189      +/-   ##
==========================================
- Coverage   85.69%   85.21%   -0.48%     
==========================================
  Files          47       72      +25     
  Lines         608     1312     +704     
==========================================
+ Hits          521     1118     +597     
- Misses         87      194     +107     

Impacted Files	Coverage Δ
demo/demoproject/settings.py	100.00% <ø> (+100.00%)	:arrow_up:
django_downloadview/middlewares.py	78.07% <100.00%> (ø)
django_downloadview/views/virtual.py	42.85% <0.00%> (-57.15%)	:arrow_down:
django_downloadview/shortcuts.py	50.00% <0.00%> (-50.00%)	:arrow_down:
django_downloadview/nginx/settings.py	76.78% <0.00%> (-19.65%)	:arrow_down:
django_downloadview/views/base.py	87.50% <0.00%> (-12.50%)	:arrow_down:
django_downloadview/views/path.py	92.85% <0.00%> (-7.15%)	:arrow_down:
django_downloadview/views/object.py	90.62% <0.00%> (-3.13%)	:arrow_down:
demo/demoproject/lighttpd/tests.py	100.00% <0.00%> (ø)
demo/demoproject/storage/tests.py	100.00% <0.00%> (ø)
... and 31 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more Δ = absolute <relative> (impact), ø = not affected, ? = missing data Powered by Codecov. Last update 0578729...2524668. Read the comment docs.